1. Field of the Invention
The present invention relates to an image processing apparatus and a control method therefor, as well as a storage medium, and more particularly, to an image processing apparatus, such as a video camera, that detects the face of a subject and performs personal identification of the detected face, and a control method therefor, as well as a storage medium.
2. Description of the Related Art
Recently, there has appeared a video camera provided with a function of personal identification in which a face is periodically detected during image pickup and compared with personal information held in advance to identify whose face it is. In the personal identification function of such a video camera, the face is identified as the face of a particular person if similarity degree calculated by comparison with the personal information is equal to or greater than a threshold set in advance. This video camera is also provided with a function of recording a moving image, attaching information about a person identified during recording of the time-varying image to the moving image. Furthermore, this video camera is provided with a function of classifying the moving image on the basis of the attached information. In the video camera provided with such functions, by specifying a person registered with the personal information, a user can extract only moving images in which the person appears.
In the personal identification function of the video camera, if the threshold for the similarity degree calculated by comparison with the personal information is set low at the time of performing personal identification, the probability of not identifying a person as the person himself (an identity rejection rate) decreases. However, at the same time, the probability of identifying a different person as the above person himself (a different person acceptance rate) rises if the threshold for the similarity degree is set low. Therefore, if the threshold for the similarity degree is set low, a result of misidentification is easily attached during recording of the moving image.
If the threshold for the similarity degree is set high, the different person acceptance rate of misidentifying a different person as a person himself lowers. However, the person himself cannot be identified, and the identity rejection rate rises. Therefore, if the threshold for the similarity degree is set high, it becomes difficult to attach a correct identification result during recording of the moving image. Thus, it is important to adjust the threshold in order to attach a personal identification result to a moving image in such a manner that the usability for a user is improved.
Among conventional face collation apparatuses, there has been proposed an apparatus for adjusting the threshold to obtain an appropriate personal identification result (see Japanese Laid-Open Patent Publication (Kokai) No. 2009-163555, for example). In this conventional face collation apparatus, the threshold is adjusted so that any of the different person acceptance rate, the identity rejection rate, the probability that the different person acceptance rate and the identity rejection rate are equal to each other can be constant irrespective of image pickup conditions such as focus and exposure and registration conditions such as the face size of registered images and the number of registered images. That is, in the conventional face collation apparatus, the threshold is adjusted so that the frequency of being identified as a person himself and the frequency of being wrongly identified are constant among all persons.
In the video camera provided with the function of personal identification, however, it is more desirable that, in the case of searching for a desired person at the time of reproducing a recorded time-varying image, the desired person has been identified with a certain degree of frequency, because the search-ability is greater. However, it is not desirable from the viewpoint of usability that misidentification is increased by giving priority to increase in the identification frequency.